Block assembly for use in metal scarfing apparatus

ABSTRACT

A block assembly for a thermochemical scarfing apparatus which allows a greater diagonal standoff distance from the metal workpiece during preheating. The block assembly comprises a base member and an extension releasably joined to the base member, and the base member and extension include an internal network of gas distribution lines for separately delivering both oxygen and fuel gas to each of a plurality of discharge openings which are disposed in a longitudinal row along the front face of the extension. A nozzle insert is releasably mounted in each discharge opening, such that during preheating, the oxygen may be discharged from each discharge opening as a central high velocity stream and the fuel gas may be discharged as a concentric stream which coaxially surrounds the central stream, and so that the momentum of the central stream is maintained. The effective flame heating distance thereby may be extended during preheating, and the block assembly may be moved back from the workpiece a significant standoff distance so as to avoid damage from dislodged molten metal slag.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 08/033,601 filed Mar. 19,1993, now U.S. Pat. No. 5,358,221, which in turn is acontinuation-in-part of applications Ser. No. 07/988,450, filed Dec. 10,1992, now U.S. Pat. No. 5,333,841; Ser. No. 07/948,027, filed Sep. 21,1992, now U.S. Pat. No. 5,304,256; and Ser. No. 07/805,111, filed Dec.9, 1991, now U.S. Pat. No. 5,234,658.

FIELD OF THE INVENTION

This invention relates to an apparatus for thermochemically scarfing ametal workpiece, and more particularly, to a block assembly for use in ascarfing apparatus of the described type and which allows a significantdiagonal stand-off distance from the end of the workpiece duringpreheating and scarfing initiation so that molten metal is not blownonto the scarfing apparatus.

BACKGROUND OF THE INVENTION

Steel slabs commonly are conditioned by moving scarfing units along thetop, bottom, and side surfaces of a steel slab to eliminate surfacedefects such as cracks, seams, and slag intrusions. One conventionalscarfing apparatus includes top, bottom, and opposite side scarfingunits that are mounted across the width and end portions of a support,to concurrently scarf all sides of the slab as the slab is passedtherebetween.

Both top, side, and bottom scarfing units all include a manifold andhead assembly, which receives and distributes oxygen and fuel gas toupper and lower preheat blocks. The upper and lower preheat blocks arespaced from each other to define between the two blocks an oxygenscarfing slot through which a quantity of oxygen is blown onto the slabsurface to enable scarfing. The lower preheat block includes a fuel gaschannel having a discharge opening positioned adjacent to the oxygenslot for discharging a fuel gas adjacent to the oxygen flow.

As illustrated for example in U.S. Pat. No. 4,115,154, the upper preheatblock typically is a one-piece unit that includes oxygen and fuel gaschannels each having discharge orifices to define nozzles through whicha combination of oxygen and fuel gas is discharged for preheating theslab before scarfing. Later, a postmix flow of oxygen and fuel gasprovides for scarfing. To maintain a proper vertical stand-off distanceof the nozzle exits from the steel slab, the top and bottom scarfingunits include riding shoes positioned on respective lower preheatblocks. Because the integrally formed nozzles do not provide for a highspeed gas flow outward from the scarfing units, the total diagonalstand-off distance, i.e., the vertical stand-off distance and horizontalstand-off distance (the lead distance from the scarfing unit to theslab) is small, and the scarfing units must be placed in close proximityto the slab during preheating. Thus, in a conventional scarfing unit asillustrated in the above referenced patent, the upper preheat blockextends forward and hangs over the lower preheat block to direct thepreheating stream of gas discharged from the upper preheat block ontothe slab during preheating.

Because the upper preheat block extends forwardly beyond the lowerpreheat block during initial preheating of the slab, the molten steelformed on the slab edge may drip onto portions of the upper preheatblock positioned below the slab. The molten steel may damage the upperpreheat block requiring reconstruction or replacement of the preheatblocks. To avoid this problem, during initial preheating, the scarfingunits are positioned adjacent to the slab and heat the slab one to twoinches inward of the end to prevent steel and slag from dripping ontothe forwardly extending preheat block. As a result of starting thescarfing process inward from the end of the steel slab, the one or twoinches of unscarfed steel must be either scrapped or hand scarfed,leading to excessive production costs.

Additionally, through continued use, the discharge ends forming theupper preheat nozzles may wear. Because the preheat nozzles areintegrally formed in the upper preheat block, any damage to the nozzlearea mandates either replacement of the entire upper preheat block, orremoval of the damaged area and the brazing of new material onto theupper preheat block.

It is an object of the present invention to provide a scarfing apparatusthat allows a greater diagonal standoff distance from the metalworkpiece during preheating and initial scarfing, and so thatsignificant quantities of molten metal are not blown onto the scarfingapparatus.

It is a more particular object of the present invention to provide ablock assembly for a scarfing apparatus which includes a number ofnozzles for directing a high speed preheating gas stream toward theworkpiece with the gas stream comprising separate streams of oxidizinggas and fuel gas, which are adapted to be ignited at a substantialdistance from the scarfing apparatus, and so that particles of moltenmetal are not blown onto the apparatus in significant quantities.

It is a further object of the present invention to provide a blockassembly for a scarfing apparatus of the described type, and whichincludes a gas distribution network internally within the block assemblyfor efficiently and effectively distributing two separate gases, namelyoxygen and fuel gas, to each of the nozzles of the apparatus.

SUMMARY OF THE INVENTION

The above and other objects and advantages of the present invention areachieved in the embodiment illustrated herein by the provision of ablock assembly for a scarfing apparatus which comprises a block ofmetallic material including opposite front and rear faces, oppositeupper and lower faces, and opposite end faces which define alongitudinal direction therebetween. A plurality of discharge openingsare positioned adjacent each other in a longitudinal row along the frontface and the openings extend rearwardly into the block a substantialdistance, and so that each opening defines an inner end which is spacedfrom the rear face of the block. A first internal bore extendslongitudinally within the interior of the block and communicates witheach of the discharge openings at a medial portion of the rearwardlength of such openings. A second internal bore extends longitudinallywithin the interior of the block and communicates with each of thedischarge openings adjacent the inner end thereof. First duct means isprovided for delivering a first gas, namely fuel gas, to the firstinternal bore, and second duct means is provided for delivering a secondgas, namely oxygen, to the second bore. Thus, the first and second gasesmay be concurrently delivered into each of the discharge openings atspaced apart locations and so that the gases flow outwardly from each ofthe discharge openings at said front face.

In the preferred embodiment, the block assembly is composed of twoseparate components, namely a rear or base member and an outer member orextension. The splitting of the block into two components permits theextension, which is subjected to the most wear, to be easily removed,repaired, and replaced at a significantly reduced cost as compared to asingle piece block.

The block assembly of the present invention further includes an elongatenozzle insert disposed in each of the discharge openings. Each nozzleinsert comprises a central bore extending axially through the lengththereof and so as to define an inner end of the central bore whichcommunicates with the inner end of the associated discharge opening andthus with the second internal bore. Sealing means is positioned tocooperate with the portion of the associated discharge opening betweenthe first and second internal bores for forming a seal between suchportion of the associated discharge opening and the outer periphery ofthe nozzle insert. A plurality of axially extending substantiallyparallel flutes are spaced about the exterior surface of the nozzleinsert and between the first internal bore and the front face of theblock and such that the flutes and the discharge opening define an outerchannel which extends from the first internal bore to the front face ofthe block. By this arrangement, the oxygen may be discharged from thecentral bore of each of the nozzle inserts as a central gas stream andwhile the fuel gas may be discharged from each of the nozzle inserts asa concentric stream disposed coaxially about the central stream.

BRIEF DESCRIPTION OF THE DRAWINGS

Some of the objects and advantages of the present invention having beenstated, others will appear as the description proceeds, when taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a partly sectioned and partly schematic side elevation view ofa scarfing apparatus which embodies the features of the presentinvention and which is positioned for preheating a steel slab before thecommencement of the scarfing operation;

FIG. 2 is a perspective and exploded view of the base member andextension of the upper preheat block assembly of the apparatus shown inFIG. 1;

FIG. 3 is a view similar to FIG. 2 but looking from the rear of theblock assembly;

FIG. 4 is a sectioned side elevation view of the block assembly andillustrating the internal gas distribution network of the assembly;

FIG. 5 is a perspective view of a preferred embodiment of the nozzleinsert adapted for use in the block assembly of the present invention;

FIG. 6 is a sectional view of the insert of FIG. 5, and;

FIG. 7 is an end view of the nozzle insert shown in FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring more particularly to the drawings, FIG. 1 illustrates ascarfing apparatus 10 which embodies the features of the presentinvention. The illustrated scarfing apparatus 10 represents the upperscarfing unit of an overall system, which typically comprises similarscarfing apparatus positioned above and below the plane of the steelslab S to be scarfed, with the upper and lower scarfing apparatusextending across the full width of the slab S. Additionally, sidescarfing apparatus of like design are positioned so as to scarf thesides of a slab S. The slab S normally is positioned on a movable rolltable (not shown) so as to be fed through the rectangular configurationdefined by the several scarfing apparatus, and in the direction of thearrow 11.

In accordance with the present invention, the scarfing apparatus 10 isconstructed to allow a significant stand-off distance from the slab Sduring preheating so that preheating can occur on the end corner of theslab without having significant amounts of slag or other hot, moltenmetal falling onto the apparatus, as occurs in other, conventionalscarfing units during initial starting adjacent the front edge of theslab.

As shown in FIG. 1, the apparatus 10 includes a manifold and headassembly 12, typically formed from a block of bronze or copper material,and the block defines a generally planar front surface 13 upon which anupper preheat block assembly 15 and a lower preheat block 16 aremounted. The block of the manifold and head assembly 12 also includes apair of internal fuel gas lines 18 and 19, a pair of oxygen lines 20 and21, and inlet and outlet water lines 22 and 23 respectively, and all ofthese lines communicate with the front surface 13 for the purposesdescribed below.

The upper preheat block assembly 15 and the lower preheat block 16 arespaced from each other to define an oxygen slot 26 and discharge orifice27 of predetermined size for receiving a flow of scarfing oxygen fromthe oxygen line 20 of the manifold and head assembly and discharging thescarfing oxygen through the discharge orifice 27 onto the steel slab Sduring the scarfing operation.

The lower preheat block 16 includes a fuel gas outlet which preferablytakes the form of a plurality of openings 28 (FIG. 4) which arepositioned adjacent the orifice 27 and are spaced apart longitudinally(i.e. in a direction perpendicular to the plane of FIG. 1) along thelength of the block. These openings 28 communicate with a fuel gasdistribution duct 30 in the block 16, which in turn communicates withthe fuel gas line 18 in the manifold and head assembly 12. Fuel gas isthus able to flow through the fuel gas flow line 18 of the manifold andhead assembly 12 into the fuel gas distribution duct 30, and then exitthrough the openings 28 to form part of a scarfing flame duringscarfing. A riding shoe 32 is mounted to the manifold and head assembly12 along the underside of the lower preheat block 16. The riding shoe 32includes a lower surface 33 having slab engaging skids 34 adapted tocontact the slab to position the scarfing discharge orifice 27 as wellas the other exiting fuel and oxygen flows a predetermined distance fromthe steel slab. As shown in FIG. 1, the scarfing apparatus 10 is abovethe slab S, and it will be understood that similar apparatus arearranged below and at the opposite sides of the slab S.

Each upper preheat block assembly 15 includes a base member 40, and anextension 42 secured to the base member 40 and extending forwardlytherefrom. The base member 40 comprises a block of metallic material,preferably copper, and it includes opposite front and rear faces 44, 45,opposite upper and lower faces 46, 47, and opposite end faces 48, 49,which define a longitudinal direction therebetween. The upper face 46includes a U-shaped channel 50 as best seen in FIG. 4, so as to define arear wall 52 and a front wall 53. The rear face 45 of the member isreleasably secured to the front surface 13 of the manifold and headassembly by means of bolts 54 which extend through the rear wall 52. Apair of dowel pins 56 extend into closed bores 57 in the rear wall tofurther secure and accurately position the base member 40 to the frontsurface 13.

The base member 40 also includes a first gas outlet in the form of anelongate channel 58 which extends longitudinally and communicates withthe front face 44 of the block, and a first gas supply duct 59 extendsthrough the block from said rear face 45 thereof to the first gas outletchannel 58. The first gas supply duct 59 in turn communicates with thefuel gas supply line 19 in the manifold and head assembly 12.

A second gas outlet in the form of a second longitudinally elongatechannel 60 communicates with the front face 44 of the block, and asecond gas supply duct 61 extends through the block from said rear face45 thereof to the second gas outlet 60. The second gas supply duct 61 inturn communicates with an oxygen supply line 21 in the manifold and headassembly.

The extension 42 comprises a block of metallic material, preferablycopper, and it includes opposite front and rear faces 62, 63, oppositeupper and lower faces 64, 65, and opposite end faces 66, 67, whichdefine a longitudinal direction therebetween. The rear face 63 of theextension includes a pair of threaded openings 68 for receiving a pairof mounting bolts 69 which extend through openings 70 the front wall 53of the base member. Also, a pair of dowel pins 71 may be secured inbores in the rear face of the extension, which are closely received inbores 72 in the front wall 53. By this arrangement, the extension 42 isreleasably and securely joined to the base member 40, with the rear face63 of the extension overlying and engaging the front face 44 of the basemember.

The extension 42 further comprises a plurality of discharge openings 74which are positioned adjacent each other in a longitudinal row along thefront face 62 and extending rearwardly into the block a substantialdistance, and so that each opening 74 defines an inner end 75 which isspaced from the rear face 63. Also each of the discharge openings has anouter portion 77 (FIG. 4) of relatively large diameter, and an innerportion 78 adjacent the inner end 75 which is of relatively smallerdiameter. A medial portion 79 of each opening 74 is internally threaded,so that each discharge opening is adapted to threadedly mount an insert100 therein which has an externally threaded inner end, and as furtherdescribed below.

A longitudinally extending row of discharge outlets 80 is provided inthe front face 62 of the extension 42, with the row of outlets 80extending parallel to and above the row of openings 74.

A first internal bore 81 extends longitudinally within the interior ofblock of the extension 42 and communicates with each of the dischargeopenings 74 at a medial portion of the rearward axial length of theopenings. A first duct means in the form of a plurality oflongitudinally spaced apart and parallel ducts 82, extends from the rearface 63 to the first internal bore 81 for delivering fuel gas to thefirst internal bore. A second internal bore 84 extends longitudinallywithin the interior of the block and communicates with the inner portion78 of each of the discharge openings 74. A second duct means in the formof a plurality of longitudinally spaced apart and parallel ducts 85,extends from the rear face 63 to the second internal bore 84 fordelivering oxygen to the second internal bore.

The relatively large diameter portion 77 of each opening 74 extendsbetween said front face 62 and the first internal bore 81, and the inner78 portion of relatively small diameter is positioned between the firstinternal bore 81 and said second internal bore 84.

Third duct means is provided for delivering the oxygen to each of thedischarge outlets. More particularly, the third duct means comprises athird internal bore 88 which extends longitudinally within the interiorof the block, first gas passage means communicating between the secondinternal bore 84 and the third internal bore 88, and second gas passagemeans extending between the third internal bore 88 and the dischargeoutlets 80. The first gas passage means comprises a plurality of bores89 which are coaxial with respective ones of the ducts 85. The secondgas passage means comprises a plurality of bores 90 which communicatewith respective ones of the outlets 80 and with the third internal bore88.

The extension 42 also includes a further internal bore 92 extendinglongitudinally within the interior of the block adjacent the front face62 thereof, and water passageway means communicating with the furtherinternal bore 92 and with the rear face 63 of the block for circulatingwater through the further internal bore 92 so as to cool the block. Moreparticularly, the water passage means comprises a water inlet line 93bore extending from the rear face 45 to the front face 44 of the basemember 40, and which communicates with the water inlet line 22 in themanifold and head assembly 12 and with a water inlet line 94 whichextends from the rear face 63 of the extension to the further internalbore 92 and parallel to the end face 67 of the block. A return line 96extends through the extension 42 and communicates with the end of thefurther internal bore 92 adjacent the end face 66. The return line 96extends to the rear face 63 of the extension 42, and communicates with afurther line 97 extending through the base member. The line 97 of thebase member in turn communicates with the water outlet line 23 of themanifold and head assembly.

When the extension 42 and base member 40 are assembled to each other,and to the manifold assembly 12, in the manner illustrated in FIG. 1, itwill be understood that the fuel gas which is delivered to the first gassupply duct 59 at the rear face 45 of the base member 40 is deliveredthrough the duct 59 to the first gas outlet channel 58 in the frontface. The channel 58 serves to distribute the fuel gas to each of theducts 82 in the rear face of the extension, under conditions ofsubstantially equal pressure along the full longitudinal length of theextension. The fuel gas is then delivered via the ducts 82 to the firstinternal bore 81, and so that the pressure along the longitudinal lengthof the bore 81 is substantially uniform. As a result, the flow rate ofthe fuel gas into the medial portion of each discharge opening 74 issubstantially uniform.

Similarly, the oxygen which is delivered to the oxygen supply duct 61 atthe rear face 45 of the base member 40 through the line 21 is deliveredthrough the duct 61 to the gas outlet channel 60 in the front face 44,and the channel 60 serves to distribute the oxygen to each of the ducts85 in the rear face 63 of the extension under conditions ofsubstantially equal pressure. The oxygen is then delivered via the ducts85 to the second internal bore 84, and then into the inner portion 78 ofeach of the discharge outlets 74. The oxygen is also delivered from thesecond internal bore 84 via the bores 89 to the third internal bore 88,and finally via the bores 90 to respective ones of the discharge outlets80 on the front face of the extension. The pressure along thelongitudinal length of each bore 84 and 88 will be substantiallyuniform, and as a result, the flow rate of the oxygen through eachdischarge opening 74 will be substantially uniform, and the flow ratethrough each discharge outlet 80 will be substantially uniform.

The internal bores 81, 84, 88, and 92 of the extension 42 may beconveniently formed by drilling longitudinally into the end face 67 ofthe extension, and to a point just short of the opposite end face 66.The resulting bores are then capped at the end face 67, as seen in FIG.3. Also, the other internal bores and ducts in the extension and thebase member may be formed by drilling operations, in a manner which willbe apparent to those skilled in the art. As a result of thisconstruction, the opposite end faces 48, 49, 66, 67 of the base memberand the extension are substantially planar, without protruding externalpiping connections or the like, and the block assembly may thus bemounted in a side by side arrangement with other like assemblies so asto form an assembly of a longitudinal length necessary to extend acrossthe full width of a slab to be scarfed.

Each discharge opening 74 mounts a nozzle insert 100, as best seen inFIGS. 2 and 5-7. In the illustrated embodiment, each nozzle insert 100is in the form of an elongate, substantially cylindrical body memberwhich is formed of a unitary piece of a metal such as brass or copper.The body member defines an outer end 101, an inner end 102, and acentral bore 103 which extends axially through the length of the nozzleinsert. The central bore 103 includes a first portion 104 adjacent theinner end of uniform diameter, a converging throat portion 105, a medialportion 106 of uniform diameter, and a diverging portion 107 adjacentthe outer end. The converging throat portion 105 tapers inward at arelatively steep angle as best seen in FIG. 6, and the diverging portion107 tapers outward at a less steep angle. When assembled in itsassociated discharge opening 74 as seen in FIG. 4, the outer end 101 ofthe insert is flush with the front face 62, and the oxygen gas which isreceived in the inner portion 78 of the opening from the second internalbore 84, is first constricted within the converging portion 105 wherethe gas velocity is increased. The oxygen then exits the outer end 101as a high velocity, preferably supersonic, accurately directed stream.

The outer or discharge end portion of each nozzle insert includes aplurality of axially directed flutes 108 spaced about the exteriorsurface, and so as to extend between the first internal bore 81 of theextension and the front face 62 of the extension. Thus the flutes 108 ofthe insert and the discharge opening 74 define an outer channel whichextends from the first internal bore 81 to the front face 62, andcoaxially surrounds the central bore 103 of the insert. The fuel gas maythereby be discharged as a concentric stream which coaxially surroundsthe oxygen stream being discharged from the central bore 103 of theinsert.

The exterior peripheral surface of each insert also includes anexternally threaded portion 110 adjacent the inner end 102. Thisthreaded portion 110 is adapted to engage the mating threaded portion 79in the cylindrical opening 74 of the block, note FIG. 4, and tofacilitate the engagement and disengagement of this threadedinterconnection, the bore of the insert is provided with a hex socket112 at the outer end 101 which is adapted to be engaged by an Allenwrench or the like. A slot may if desired be substituted for the hexsocket, to permit engagement by a conventional screwdriver.

The insert 100 also includes a pair of spaced apart shoulders 114, 115positioned axially between the flutes 108 and the externally threadedportion 110, and so as to form an annular channel 116 therebetween whichis adapted to receive a resilient O-ring 118. The rearward shoulder 115also includes a rearwardly facing frusto-conical surface portion 120which is adapted to form a metal to metal seat with a mating surface inthe cylindrical opening 74 of the block of the extension. The metal tometal seat and the O-ring 118 thus form a seal which precludes gaspassage through the discharge openings 74 between the first and secondinternal bores 81 and 84.

During operation, the apparatus 10 is initially positioned as shown inFIG. 1, together with bottom and side scarfing units (not shown), andthe flows of oxygen and fuel gas through the various passageways arecontrolled to initially preheat the slab S. Because the nozzle insert100 provides an efficient oxygen and fuelgas flow outward from theapparatus 10 without a sharp fuel gas flow intersection with the oxygenadjacent the nozzles, the momentum of the oxygen exiting the centralbore 103 of each insert is maintained until it intersects the fuel gasfurther downstream from the extension. As a result, a more enhanced andhotter flame is achieved, and the diagonal standoff distance may beincreased as compared to other conventional scarfing apparatus. With thepresent invention, a diagonal standoff distance as high as fifteeninches has been achieved. As a result of this greater diagonal stand-offdistance, during initial pre-heating of the slab S, significant amountsof the slag and molten steel do not drop onto the apparatus and thescarfing operation can begin at the end portion of the slab.Additionally, during continued use of the apparatus, the outer ends 101of the nozzle inserts 100 may become worn. The nozzle inserts 100 can bereadily replaced by simply unthreading them from their associateddischarge openings, and a new nozzle insert may then be inserted andthreaded into its assembled position.

The steps involved in the initial starting of the scarfing process aredescribed in detail in copending application Ser. No. 07/988,450. Tobriefly summarize, the table (not shown) on which the steel slab S restsis moved into a position in which the scarfing apparatus 10 ispositioned over and adjacent an end of the slab. The scarfing apparatuspreheat fuel gas is then ignited at a low flow rate, and the preheatoxygen is also discharged at a low flow rate. Also, a small volume flowof oxygen is concurrently directed through the scarfing slot 26 toprovide a lower shield flow, note FIG. 4. The preheat fuel gas flow rateis then increased, and just after the preheat fuel gas flow rate isincreased, the oxygen preheat flow is increased, and this flow includesa stabilizing oxygen stream immediately above the preheating gas streamemanating from the discharge outlets.

In one preferred embodiment, the central stream of oxygen is dischargedfrom each central bore 103 of the inserts 100 at a substantiallysupersonic speed, and the concentric stream of fuel gas is discharged ata speed less than the speed of the central stream. Also, the upper andlower oxygen stabilizing streams are discharged at respective speedswhich are less than the speed of the stream of fuel gas.

Once the steel slab is preheated, the preheat oxygen flow issubstantially reduced and the flow of scarfing oxygen is generatedthrough the slot 26. When the scarfing oxygen has reached its peakpressure and flow rate, the preheating fuel gas is reduced, and thetable holding the steel slab is moved toward the scarfing apparatus. Thetable is initially moved forward at a first relatively slow speed, whichis typically about 3 to 4 meters per minute, and after a predeterminedperiod, its speed is increased to the normal scarfing speed, which isabout four times as fast as the first speed. The flow rate of the oxygenis decreased slightly at the time when the table speed reaches thenormal scarfing speed. Scarfing then continues, and preferably a streamof fuel gas is concurrently discharged from the discharge end of thefuel gas outlet opening 28 of the lower block 16, to facilitatemaintenance of the oxidizing reaction. Also, the manifold and headassembly 12 closes so that the skids 34 move into contact with themoving slab S, and the entire apparatus 10 "floats" on the moving slab.

In the drawings and specification, there has been set forth a preferredembodiment of this invention, and even though specific terms are used,they are used in a generic and descriptive sense only and not forpurposes of limitation.

That which is claimed is:
 1. A block assembly for directing multiplestreams of gas onto the surface of a metal workpiece during a scarfingoperation, and comprisinga block of metallic material including oppositefront and rear faces, opposite upper and lower faces, and opposite endfaces which define a longitudinal direction therebetween, a plurality ofdischarge openings positioned adjacent each other in a longitudinal rowalong said front face and extending rearwardly into said block asubstantial distance, and so that each discharge opening defines aninner end which is spaced from said rear face, first duct meansextending within the interior of said block and communicating with eachof said discharge openings at a medial portion of the rearward length ofsaid openings and also communicating with said rear face of said block,second duct means extending within the interior of said block andcommunicating with each of said discharge openings adjacent the innerend thereof and also communicating with said rear face of said block,whereby a first gas may be delivered to said first duct means at saidrear face of said block and a second gas may be delivered to said secondduct means at said rear face of said block, and the first and secondgases may be concurrently delivered into each of said discharge openingsat spaced apart locations and so that the gases flow outwardly from eachof said discharge openings at said front face.
 2. The block assembly asdefined in claim 1 wherein each of said discharge openings has a portionof relatively large diameter between said front face and said medialportion of the discharge opening, and a portion of relatively smalldiameter between said medial portion and said inner end of the dischargeopening.
 3. The block assembly as defined in claim 2 wherein saidportion of relatively small diameter of each discharge opening isinternally threaded so that each discharge opening is adapted tothreadedly mount an insert therein which has an externally threadedinner end.
 4. The block assembly as defined in claim 1 furthercomprising discharge outlet means extending longitudinally along saidfront face of said block and parallel to said row of discharge openings,and third duct means extending within the interior of said block andcommunicating with said second duct means for delivering the second gasto said discharge outlet means.
 5. The block assembly as defined inclaim 4 wherein said discharge outlet means comprises a row of dischargeoutlets which is parallel to said row of discharge openings.
 6. Theblock assembly as defined in claim 1 further comprising an internal boreextending longitudinally within the interior of said block adjacent saidfront face thereof, and water passageway means communicating with saidinternal bore and with said rear face of said block for circulatingwater through said internal bore so as to cool the block.
 7. The blockassembly as defined in claim 1 further comprising an elongate nozzleinsert disposed in each of said discharge openings, with each of saidnozzle inserts comprising a central bore extending axially through thelength thereof and so as to define an inner end of said central borewhich communicates with said inner end of the associated dischargeopening and thus with said second duct means, sealing means forming aseal between the portion of the associated discharge opening betweensaid medial portion and said inner end thereof and the outer peripheryof the nozzle insert, a plurality of axially extending substantiallyparallel flutes spaced about the exterior surface of the nozzle insertand between said medial portion of the discharge opening and said frontface of said block and such that the flutes and the discharge openingdefine an outer channel which extends from said medial portion of thedischarge opening to said front face of said block, whereby the secondgas may be discharged from said central bore of each of said nozzleinserts as a central gas stream and while the first gas may bedischarged from each of said discharge openings as a concentric streamdisposed coaxially about said central stream.
 8. A block assembly fordirecting multiple streams of gas onto the surface of a metal workpieceduring a scarfing operation, and comprising:a base member comprising(a)a block of metallic material including opposite front and rear faces,(b) a first gas outlet communicating with said front face of said block,and a first gas supply duct extending through said block from said rearface thereof to said first gas outlet, (c) a second gas outletcommunicating with said front face of said block, and a second gassupply duct extending through said block from said rear face thereof tosaid second gas outlet, and an extension comprising(a) a block ofmetallic material including opposite front and rear faces, oppositeupper and lower faces, and opposite end faces which define alongitudinal direction therebetween, (b) a plurality of dischargeopenings positioned adjacent each other in a longitudinal row along saidfront face and extending rearwardly into said block a substantialdistance, and so that each discharge opening defines an inner end whichis spaced from said rear face, (c) first duct means extending within theinterior of said block and communicating with each of said dischargeopenings at a medial portion of the rearward length of said openings andalso communicating with said rear face of said block, (d) second ductmeans extending within the interior of said block and communicating witheach of said discharge openings adjacent the inner end thereof and alsocommunicating with said rear face of said block, means interconnectingsaid extension and said base member with said rear face of saidextension overlying and engaging said front face of said base member,and such that said first gas outlet of said base member communicateswith said first duct means of said extension and said second gas outletof said base member communicates with said second duct means of saidextension, whereby a first gas may be supplied to said first gas supplyduct of said base member and delivered to said first duct means of saidextension, and a second gas may be supplied to said second gas supplyduct and delivered to said second internal bore of said extension. 9.The block assembly as defined in claim 8 wherein said first duct meanscomprises a plurality of longitudinally spaced apart parallel ducts insaid extension.
 10. The block assembly as defined in claim 9 whereinsaid second duct means comprises a plurality of longitudinally spacedapart parallel ducts in said extension.
 11. The block assembly asdefined in claim 8 wherein said extension further comprises dischargeoutlet means extending longitudinally along said front face of saidblock of said extension and parallel to said row of discharge openings,and third duct means extending within the interior of said block andcommunicating with said second duct means for delivering the second gasfrom said second duct means to said discharge outlet means.
 12. Theblock assembly as defined in claim 8 wherein said extension furthercomprises an elongate nozzle insert disposed in each of said dischargeopenings, with each of said nozzle inserts comprising a central boreextending axially through the length thereof and so as to define aninner end of said central bore which communicates with said inner end ofthe associated discharge opening and thus with said second duct means,sealing means forming a seal between the portion of the associateddischarge opening between said medial portion and said inner end thereofand the outer periphery of the nozzle insert, a plurality of axiallyextending substantially parallel flutes spaced about the exteriorsurface of the nozzle insert and between said medial portion of thedischarge opening and said front face of said block of said extensionand such that the flutes and the discharge opening define an outerchannel which extends from said medial portion of the discharge openingto said front face of said block of said extension, whereby the secondgas may be discharged from said central bore of each of said nozzleinserts as a central gas stream and while the first gas may bedischarged from each of said discharge openings as a concentric streamdisposed coaxially about said central stream.